Water reducible, or water dilutable, resin compositions can be prepared by the aqueous emulsion polymerization of a manipulated and balanced mixture containing a major portion of hydrophobic enhancing monomers and a minor portion of hydrophilic enhancing monomers. A singular primary advantage of such resins is their departure from a primary dependence upon organic solvents for producing coatings therefrom, thereby enabling coating preparations for various substrates with a much reduced heretofore inherent potential toxicity, flammability and environmental pollution.
It should be appreciated that such aqueous emulsion polymerizations could conveniently be conducted with the aid of typical emulsifiers to suspend or emulsify the monomers and polymers resulting therefrom, following which the polymers could simply be coagulated by the addition of a coagulant such as aluminum sulfate. An inherent disadvantage in such a polymerization and emulsion system for a water reducible resin is that a water-deposit coating thereof on the resin carries with it the water-sensitive emulsifier products. Thus, when the coalesced coating is dried, thereby becoming essentially water-insoluble, the hydrophilic emulsifier products remain to attract water to the coating and promote its degradation.
Therefore, it is an object of this invention to provide a resin formed by aqueous emulsion polymerization which can conveniently be dispersed or dissolved in an aqueous medium to form a suitable coating composition and a coating resulting therefrom without the disadvantage of containing hydrophilic surfactant residue.
A particular advantage of water dilutable (reducible) resins made with a minimal amount of a polymerizable surfactant is that such a resin can be isolated from its latex by spray drying. In such a process, the resin is recovered in powder form directly from its latex without the typical necessity of coagulating filtering and grinding before packaging. Conventional emulsion-promoting surfactants used in conventional resin preparation by latex technique generally leave water soluble residue on the spray dried resin with very poor water resistance.